Device at grate means mounted in a mill or another processing apparatus

ABSTRACT

A screening device for a grinding mill comprising a plurality of radially extending elastic polymeric sectors having openings therein together with a plurality of clamping members for clamping the radially extending edges of said sectors to a portion of the grinding mill framework, and sector support means disposed between each sector and the portion of the mill framework to which the sector is attached by said clamping means, each sector support means being composed of rigid material and being constructed of a pair of radially extending rigid bars adapted to fit under the radially extending edges of a sector and a plurality of rigid cross bars extending between said pair of radially extending rigid bars, whereby each sector support means will support an elastic polymeric sector across the area between its radially extending edges and thereby decrease the tendency of the sector to bulge.

United States Patent J onsson July 15, 1975 [75] Inventor: Elis Jonsson, Ersmark, Sweden [73] Assignee: Skega Aktiebolag, Ersmark, Sweden [22] Filed: July 20, 1973 121] Appl. No.: 381,201

{30} Foreign Application Priority Data Aug. 2, 1972 Sweden 10063/72 [52] US. Cl. 241/70; 241/181; 241/300 [51] Int. Cl. B02c 17/02 [58] Field of Searchlm..." 241/70. 71, 79, 171, 179,

[56] References Cited UNITED STATES PATENTS 1405,6311 8/1946 Barker .4 241/171 X 3.21 L387 10/1965 Russell et a1 241/183 X 3.219284 11/1965 Fahlstrom et a1 241/70 3,599,882 8/1971 Sabaski 241/70 3 604 637 9/1971 Sabaski 241/70 3.6041139 9/1971 Jenness 241/182 Primary Examiner-Roy Lake Assistant ExaminerHoward N. Goldberg Attorney, Agent, or FirmFred Philpitt [5 7] ABSTRACT A screening device for a grinding mill comprising a plurality of radially extending elastic polymeric sectors having openings therein together with a plurality of clamping members for clamping the radially extending edges of said sectors to a portion of the grinding mill framework, and sector support means disposed between each sector and the portion of the mill frame work to which the sector is attached by said clamping means, each sector support means being composed of rigid material and being constructed of a pair of radially extending rigid bars adapted to fit under the radially extending edges of a sector and a plurality of rigid cross bars extending between said pair of radially extending rigid bars, whereby each sector support means will support an elastic polymeric sector across the area between its radially extending edges and thereby decrease the tendency of the sector to bulge.

1 Claim, 5 Drawing Figures l DEVICE AT GRATE MEANS MOUNTED IN A MILL OR ANOTHER PROCESSING APPARATUS Mills used in the concentration industry and other industries for grinding minerals often are provided with a grate means at the discharge end in order to render possible, together with grate discharge means arranged behind the grate means in the feed direction, a higher outflow rate of ground material. The foremost object of these grate means is to allow the ground material to pass through and at the same time to retain the grinding medium, for example balls or so-called pebbles, in its place within the rotary part of the mill.

Grate means of this kind for mills and other mineral processing apparatus were for many years manufactured exclusively of steel in the form of plates with throughput apertures. It was first in conjunction with the development of rubber lining in mills that experiments were started to manufacture also the grate means of the same material as the linings. At first these grate means were built up about a steel structure, which was vulcanized into the rubber, but rather soon an abnormally heavy wear was observed just above the vulcanized reinforcement. The reason thereof was found to be the fact that rubber is worn much more rapidly when it is applied in such a rigid manner that its elasticity cannot be fully utilized for taking up energy from the wearing material.

In order to eliminate this heavy wear, an experiment was then made with rubber grate means without any reinforcement. This experiment, however, did not show the desired result, either, because it was found that such rubber grate means do not withstand the high pressures occurring in mills of the aforesaid kind. Thereafter rubber grate means were applied which were provided with a cord reinforcement laid therein and with a steel frame vulcanized about the edges of the plates. Hereby one had succeeded in combining the necessary strength with some form of elasticity and in making the grate means sufiiciently stable for being carried. The disadvantage of this grate construction is that the grate plates cannot be prevented from bulging.

The present invention, therefore, has as its object to eliminate above all the disadvantages involved with the known rubber grate means and to render possible the use of a grate means comprising plates of a polymer material without steel reinforcement so as to be able to utilize the elasticity of the polymer material and other advantages thereof, e.g. with respect to clogging. This object is achieved in that the device according to the invention shows the characterizing features defined in the claims.

The invention is described in greater detail in the following, with reference to the accompanying drawings, in which FIG. 1 shows a perspective view of a grate means arranged according to the invention for a relatively small ball mill, certain parts comprised in the grate means being moved apart and other parts being removed for the sake of clarity.

FIG. 2 shows a section along the line 11-]! in FIG. 1,

FIG. 3 shows a plane view ofa supporting frame comprised in the device according to the invention for a grate means of a larger type than that shown in FIG. 1,

FIG. 4 shows a plane view of a portion of a grate means, the supporting frame shown in FIG. 3 mounted in place, and

FIG. 5 shows a section along the line V-V in FIG. 4.

Referring to FIG. 1, I designates a grate means assembled of a plurality of plates 2 consisting of a polymer material without steel reinforcement. These plates 2 are clamped in a manner known per se against radially arranged supporting surfaces 3 by means of lifters 5 provided on the discharge side of the grate means. Each one of said lifters 5 overlaps two adjacent plates 2 and is provided with a longitudinal recess 12 for receiving a fastening rib 13 having bolts 14 for the performance of the clamping. Said supporting surfaces 3 are connected to grate discharge means 4 on the discharge side of the grate means. According to the invention, below each grate plate 2 a supporting frame 6 of e.g. steel or another equivalent material is mounted. Each such frame is supported by two adjacent supporting surfaces 3 and retained in position by the grate plate 2 mounted thereabove, without any connection between the same relative one another. In other words: each grate plate 2 is to be placed loosely on the supporting frame 6 therebelow and then being clamped in pairs, in position on the frame 6, i.e. on the frame members 7, together with said frame 6 and the lifters by tightening the bolts 14.

The supporting frame 6 for a plate comprises two longitudinal supporting bars 7 adapted to lie below the longitudinal edge portions of a plate and entirely to the side of fields of throughput apertures of the plate marked schematically in FIGS. 1 and 4 by rectangular squares 8 in order not to obstruct the throughput of ground material. The two supporting bars 7 are inter connected by means of narrow cross-bars 9, the surface 10 of which lies in the same plane as the surface of the supporting bars facing the plate, and which are adapted to support the grate plate between the supporting bars in order to prevent them from deflecting. The number of such cross-bars may vary from one case to the other, depending on the length and tapering degree of the grate plates. In FIGS. 1 and 2, for example, supporting frames are shown which are provided with three crossbars though both a greater and smaller number may be used while the supporting frame shown in other FIGS. and intended for a larger grate plate 2 mounted against a transverse lifter 11 (see particularly FIGS. 4 and 5) has four such cross-bars. The last-mentioned supporting frame, moreover, differs from that shown in FIGS. 1 and 2 by its supporting bars having the form of angular irons instead of flat irons.

By placing according to the invention frames of steel or another equivalent material as a support behind the grate plates in a grate means and not securing the respective frame and plate relative one another, a grate means is obtained which lies plane and does not show any tendency of bulging, at the same time as the flexibility of the polymer material is maintained so that the grate means is worn uniformly over its entire surface and a heavy local wear as in the case of grate means with vulcanized steel reinforcement is avoided. Furthermore, by designing the supporting frame somewhat shorter than the plate proper, it is possible to adjust the plate in radial direction so as not to cover any throughput aperture.

I claim:

I. In the known type of screening device which is adapted to be disposed transversely across the longitudinal axis of a grinding mill and which screening device comprises a plurality of radially extending elastic poly-, Y

rigid material and being constructed of a pair of radially extending rigid bars adapted to fit under the radially eiitending edges of a sector and a plurality of rigid cross bars extending between said pair of radially extending rigid bars, whereby each sector support means will support an elastic polymeric sector across the area between its radially extending edges and thereby decrease the tendency of the sector to bulge. 

1. In the known type of screening device which is adapted to be disposed transversely across the longitudinal axis of a grinding mill and which screening device comprises a plurality of radially extending elastic polymeric sectors having openings therein for the passage of certain size material together with a plurality of clamping members for clamping the radially extending edges of said sectors to a portion of the grinding mill framework, the improvement in said known combination which includes sector support means disposed between each sector and the portion of the mill framework to which the sector is attached by said clamping means, each sector support means being composed of rigid material and being constructed of a pair of radially extending rigid bars adapted to fit under the radially extending edges of a sector and a plurality of rigid cross bars extending between said pair of radially extending rigid bars, whereby each sector support means will support an elastic polymeric sector across the area between its radially extending edges and thereby decrease the tendency of the sector to bulge. 